Electrocardiogram (ECG) monitoring has been widely used on adult patients for detecting medical conditions, for example, abnormities associated with the heart. Signals representing a patient's cardiac activities can be collected through a set of skin surface electrodes distributed over the patient's body, for example, attached to the patient's chest and limbs.
Monitoring of fetal ECG can be difficult due to the co-existence of maternal and fetal signals in raw signals acquired from a patient, as well as the relatively low fetal signal level relative to the maternal signal and other noise sources. Some conventional approaches to collecting fetal ECG signals include placing a wire electrode onto the fetal scalp. Although the fetal scalp electrode may provide a relatively clean fetal signal, this procedure can only be performed under limited clinical circumstances (e.g., when a patient is in labor, has ruptured amniotic membranes, and has a dilated cervix) and thus may not be suitable for the vast majority of pregnant and laboring patients. The placement of the fetal scalp electrode may also present certain risks to fetal safety, as rare cases of fetal scalp abscess and newborn death have been reported.